1. Field of the Invention
The present invention relates to a light emitting device and a method of driving the same, particularly relates to a light emitting device without cross-talk phenomenon and a method of driving such light emitting device.
2. Description of the Related Art
An organic electroluminescent device is a light emitting device, which emits light with a certain applied voltage thereto.
FIG. 1A is a block diagram illustrating an organic electroluminescent device; and FIG. 1B is an equivalent circuit diagram of some of the pixels of FIG. 1A.
Referring to FIG. 1A, an organic electroluminescent device is comprised of a panel 100, a scan driving circuit 102, a data driving circuit 106 and a controller 104.
The panel 100 includes a plurality of pixels E11 to E44 that are defined as overlying areas of data lines D1 to D4 and scan lines S1 to S4.
For example, the pixels E11 to E44 of the panel will emit light in the case that a voltage 20V is applied to the data lines D1 to D4 and a voltage 0V is applied to the scan lines S1 to S4.
In this case, some of the pixels E11 to E44 may not emit light for various reasons. For example, when some of the pixels E33 to E43 located on a third scan line S3 are set not to generate light at a certain time, the total current value passing through the third scan line S3 becomes less than the total current value passing through the other scan lines S1, S2 and S4.
Conventionally, the organic electroluminescent device provides the scan lines S1 to S4 with scan signals of the same low logic value, for example 0V, in sequence. Thus, it is appreciated that the same voltage, e.g. 20V is applied between the cathode and the anode of each pixel if the electroluminescent device normally operates.
However, in reality, different voltages are applied to the cathodes of the luminescent (luminescent) pixels because of the combined effect of the line resistance (for example 160Ω) of the scan lines and some non-luminescent pixels E33 and E43.
As a result, the voltages applied between the cathode and the anode of the pixels may be different from each other, and thus the pixels emit light at different luminance even though they are predetermined to have the same luminance value. Such phenomenon is referred to as cross-talk.
For example, let's assume that the total current passing through the first scan line S1 is 14 mA, and that of the third scan line S3 is 10 mA because of the non-luminescent pixels E33 and E34. Here, the first pixel E11 and the third pixel E13 are preset to emit light at the same luminance in a normal state.
In this case, since the line resistance of each scan line S1 to S4 is 160 Ω, the voltage difference between the cathode and the anode of the first pixel E11 on the first scan line S1 is 20V(Vcc)−0V(the voltage of the first scan signal)−2.24V(14 mA×160Ω, the voltage of the first scan line S1)=17.76V. In comparison, the voltage difference between those of the third pixel E13 on the third scan line S3 is 20V(Vcc)−0V(the voltage of the third scan signal)−1.6V(10 mA×160Ω, the voltage of the third scan line S3)=18.4V.
Namely, the voltage difference between the cathode and the anode of the luminescent pixels on the third scan line S3 is larger than the voltage difference of the pixels on the other scan lines S1, S2 and S4 which are preset to emit light at the same luminance. As a result, the luminescent pixels on the third scan line S3 emit light with higher luminance than the pixels on the other scan lines S1, S2 and S4 do.
In short, such luminance variation occurs adversely to the designer's intention between the pixels due to the above described cross-talk phenomenon.
Although the organic electroluminescent device is taken as an example in the foregoing description, the cross-talk is a common phenomenon encountered in other light emitting devices. Therefore, there is a need to develop a light emitting device and method of driving the same where such cross-talk problem may be solved.